(a) Technical Field
The present invention relates to a system and method for charging a high voltage battery for a vehicle, and more particularly, to a system and method that can increase fuel efficiency by charging a battery with optimum power conversion efficiency.
(b) Description of the Related Art
In a topology in which an isolated DC-DC converter with a full-bridge or half-bridge structure is used, a maximum duty must be used. An output voltage at a Power Factor Correction (PFC) converter of a slower charger which is mounted on a vehicle is controlled to be maintained at a constant value. However, when a charged voltage of a battery is low, the maximum duty cannot be used in the isolated DC-DC converter. Accordingly, a significant conduction loss occurs due to a freewheeling current. This problem significantly deteriorates the overall efficiency of a slower charger, resulting in an increase in charging time.
In particular, when the output voltage of the PFC converter of a slower charger is controlled to be maintained at a predetermined constant value, a voltage of a battery connected to an output terminal of a DC-DC converter of the slower charger depends on a State of Charge (SOC). Since the voltage of the battery fluctuates within a large range when the battery is charged, if the output voltage of the PFC converter is maintained at a constant value, the efficiency is decreased. The decreased average charging efficiency of the slower charger leads to a decrease in Miles Per Gallon of gasoline equivalent (MPGe) and an increase in charging time.
FIG. 1 (RELATED ART) illustrates a battery charging system according to a conventional art. With reference to FIG. 1, a battery charging system 100 includes an alternating current input power supply 100, a PFC converter 120, a DC-DC converter 130, a high voltage battery 140, and a controller 150. The controller 150 transmits a voltage fixing command to the PFC converter 120 so that the output voltage of the PFC converter 120 can be fixed.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.